Public Accountant = Contadora Pública (note that I used the feminine forms)
Soy contadora. = I'm an accountant.
Soy Contadora Pública. = I'm a Public Accountant.
The Certified part of your title will vary from country to country (what's new?). It could be any of these:
Contadora Pública ...
... Certificada
... Titulada
... Autorizada
... Matriculada
... Colegiada

In Spain, they may even say contable instead of contadora.